本文从隧道施工中实测，获得III、IV、V类围岩超欠挖样本参数，通过数理统计分析给出了各类围 岩超欠挖的数宇特征及概型分布，同时得出了各类围岩下超欠挖在隧道断面不同部位的分布规律.作为隧道施工质量控制和隧道结构可靠性研究的参考。

Based on the practical measurements during tunnel construct ion, the specimen parameters of over-excavating and under-excavating for E，IV﹠V scries of surrounding rocks arc obtained. The numerical characteristics and the probability distributions of over-excavating and under-excavating for different series of surrounding rocks are put forward through numerical and physical statistics and analyses.At the same time,the law of distribution of over-excavating and under-excavating at different portion on tunnel section for different series of surrounding rocks are also obtained,which may be used for controlling the quality of construction and taken as reference for researching the reliability of the tunnel Structure.